In the oil and gas industry, following drilling of a well, or portion of a well, there is a need to re-enter the drilled openhole portion of the wellbore, for the installation of casing or cementing strings. Local deviations in the raw drilled formation of the wellbore can impede such re-entry, such deviations including wellbore eccentricity, washout and debris. In rotating strings the risk imposed by such deviations in minimal, however, at the end of a long string, in particular at high build sections or horizontal well portions, the conveyance string is not rotatable, or rotation is discouraged. In such cases, there is a high risk that the string cannot progress past the obstruction or deviation.
While casing strings have been rotated to assist with moving past or through an obstruction, high torque created by trying to rotate a long string of casing may result in significant damage to the threads between casing joints and may cause centralizers and the like to drag and ream into the wellbore. While rotation of casing may be a viable option in a vertical wellbore, albeit fraught with problems, it is extremely difficult, if not impossible in a horizontal wellbore.
Thus, the normal means for overcoming such impediments, such as rotation of the entirely of the string for rotation of the distal end, bit or other leading edge, are not available. A downhole tool inserted into the lateral borehole could engage a discontinuity and, in long non-rotating strings, could be difficult to overcome and be unable to run in any deeper and operations frustrated.
Further, In the oil and gas industry, following drilling of a wellbore into a formation for the production of oil or gas therethrough, the wellbore is typically cased and cemented to line the annular length of the wellbore for ensuring safe control of production of fluids therethrough, to prevent water from entering the wellbore and to keep the formation from “sloughing” or “bridging” into the wellbore. Cementing procedures often employ a cementing tool such as a float shoe or a float collar disposed along a casing string for conducting cement into the wellbore and back up along the annulus between the casing and the drilled wellbore.
The cementing tool typically has a mechanism that prevents reverse flow of wellbore fluids into the casing while the casing is run in and also prevents reverse flow of cement slurry from the annulus into the casing after cement is injected. In some cases, this mechanism can be in the form of an internal check valve, and in some other cases, this mechanism can be in the form of an actuable sleeve that opens and/or closes ports on the cementing tool.
For example, U.S. Pat. No. 7,617,879 to Anderson teaches a casing shoe that attaches to a downhole end of a casing string. Anderson's casing shoe has an internal check valve that is biased by a spring to remain closed during running in of the casing string. The check valve is then opened by a pressure created by a cement slurry being injected downhole. The casing string is not equipped to overcome obstructions and may not land at the desired target depth.
It is well known that during the running in of the casing in horizontal wellbores as well as in vertical wellbores, particularly production casing, the casing string may encounter obstructions in the wellbore, such as that created by sloughing of the wellbore wall into the open hole or as a result of the casing pushing debris ahead of the bottom end of the casing along the open hole until it forms a bridge. Such obstructions prevent the advance of the casing and require the open hole to be cleared in order to advance the casing to the bottom of the hole.
Typically this requires running a separate drilling string downhole to attempt to clear the obstruction then trying once again with the cementing string. Thus in alternative approach, others have contemplated providing obstruction-engaging teeth, such as a drill bit, on the bottom of the casing string or on a shoe at the bottom of the casing string to assist with cutting away the obstruction as the casing is advanced during running in.
As known in the industry, cementing tools are not equipped with the ability to drill or otherwise be used to remove such obstructions. Accordingly, should the casing string becoming sufficiently engaged in a mud pack formed at the obstruction, differential sticking may occur making or removal of the casing from the wellbore extremely difficult and certainly advancing improbable.
U.S. Pat. No. 7,757,764 to Vert et al. discloses a float collar disposed along a casing string and having a drilling assembly running therethrough. Upon completion of drilling operations, the drilling assembly is removed from the wellbore, such as through the casing string, and a cement float can be placed downhole to engage the float collar, after which cement slurry can be pumped in. In order to manage both drilling and cementing separate runs are required to change strings.
Also, while it is known casing strings may be rotated to assist with moving past or through an obstruction, high torque created by trying to rotate a long string of casing may result in significant damage to the threads between casing joints and may cause centralizers and the like to drag and ream into the wellbore. Typically, when an obstruction is encountered, drilling fluids are pumped through the casing while the casing is being reciprocated. The fluids act on the debris in the wellbore in an attempt to wash out the debris and lift it up the annulus to surface. Should the washing technique be unsuccessful, it is known to trip out the casing and run in a mud motor on a drill string to clear the obstruction from the wellbore. Such repeated running in and tripping out is time consuming, labor intensive and, as a result, very expensive. Thus, there have been tools applied at the distal end of the casing that enable clearing of obstructions without casing rotation.
For example, U.S. Pat. No. 8,191,655 to Declute-Melancon teaches a tool that can be axially reciprocated by the casing string to actuated a drill bit attached thereto for drilling out obstructions. In cases where a wellbore obstruction is encountered during cementing operations, the cementing operations would have to be delayed to allow the tool to be run in to clear the obstruction. Once the obstruction is cleared, the casing string would have to be tripped out and the cementing operations restarted.
Similarly, as shown in FIG. 1A and as set forth in Applicant's issued U.S. Pat. No. 8,973,682 issued on Mar. 10, 2015, a tool is disclosed for clearing out wellbore obstructions using axial reciprocation of the casing string. The tool is limited to clearing, but is not able to aid with cementing.
An aspect about cementing operations is that one cannot afford the expense of accidental incursion of cement back into the casing string, the bore of the casing string being reserved for production and other tools related to fracturing and production. Once again, if cement were to backflow into the casing, a separate expensive drilling run would be required to remove the wayward cement. Both the Declute-Melancon and Applicant's obstruction-clearing tools are vulnerable to cement leakage from the annulus, through the tool rotation mechanisms and back into the casing.
The conventional methodology and apparatus is unable to deal with problems such as both clearing obstruction during run in and competently enabling cementing operations. Ideally, what is required is a relatively simple and inexpensive apparatus that can be incorporated into the casing string during a cementing run for both clearing wellbore obstructions without the need for rotating the casing string. Ideally, the apparatus could be left downhole, after the casing and cementing operations are complete, and later be drilled out, without a significant increase in operational costs.